Funds are requested to purchase a Waters Synapt G2-Si mass spectrometer that will provide new capabilities to researchers on the Berkeley campus, on other University of California campuses and other researchers outside of the UC system. This instrument will be part of the QB3/Chemistry Mass Spectrometry Facility with Profs. Williams, Healy, Portnoy, Rappaport, and Raymond as major users and Prof. Coates as a minor user of the instrument, and approximately 14 other research groups who would likely benefit from the capabilities of this instrument as well. The Mass Spectrometry Facility serves a local UC Berkeley community of about 75 chemistry and life sciences research laboratories. The requested instrument features ion mobility separation, which is currently not available in our facility or at any other laboratory on the Berkeley Campus. The Synapt will support a wide range of research activities focusing on separating isomers, isoforms, and isobaric compounds. When combined with high- performance tandem MS, ion mobility separations will allow us to differentiate samples by size, shape and charge as well as mass. Additionally the ion mobility feature of the Synapt appears to be well suited for the analysis of complex proteomics samples, i.e., proteolytic digests of complex protein mixtures. In particular, the unique ability of the ion mobility analyzer to separate peptide ions that overlap in the mass-to-charge ratio (m/z) dimension but which have different charge states produces dramatic improvements in overall proteome coverage. Project descriptions including preliminary from five major users and one minor user are provided to support our need for this instrument. This instrument will be housed in a QB3 Core Service Facility that will ensure its widest availability and most effective use in our research community. We are confident the addition of the Synapt G2-Si will significantly improve our ability to assist researchers within the life science community solve complicated research projects requiring advanced mass spectrometric equipment.